Siphon in, siphon out - risks?

[AquaPin]

Do not think it will work, you are going to need pumps in and out or an overhang for the return.

*Syphons work on differences of pressure created by differences in height. The pressure difference is minuscule but it is enough to get the flow started, and keep it going. Once the heights are the same, there is no pressure difference, hence no flow.* - Yahoo

[gregzz4]

The siphon will work if I understand your plan
The line to the sump will be enough
But, you need to be able to stop it when the return pump is off, so I'd suggest you don't do it unless you look into setting it up the same as a hang-on back overflow box with an in DT box, u-tube from box to fuge, and something like a Tom's aqualifter to restart the siphon after a pump restart
I'd also use a valve on the drain line to the sump so you can dial in the flow rate through the fuge

Have a look into how hang on overflow boxes work before you buy any parts